CN113525500A

CN113525500A - Extendable shaft

Info

Publication number: CN113525500A
Application number: CN202110422862.3A
Authority: CN
Inventors: 根津俊洋; 田野淳; 辻直贵
Original assignee: JTEKT Corp
Current assignee: JTEKT Corp
Priority date: 2020-04-22
Filing date: 2021-04-19
Publication date: 2021-10-22
Also published as: EP3901483A1; US20210332855A1; JP2021173307A

Abstract

An extendible shaft (5), comprising: an inner shaft (35) comprising a plurality of external teeth (41); an outer shaft (36), the outer shaft (36) including a plurality of internal teeth (39) that slide relative to the external teeth (41); and a resin layer (50) covering the external teeth (41). The pressure angle of the external teeth (41) is different from the pressure angle of the internal teeth (39).

Description

Extendable shaft

Technical Field

The present invention relates to an extendable shaft.

Background

Japanese patent application publication No.2014-238173 discloses an extendable shaft integrated in a vehicle steering device. The extendable shaft is formed by fitting an inner shaft having a plurality of external teeth and a cylindrical outer shaft having a plurality of internal teeth by means of splines so as to be able to slide in the axial direction and transmit torque. A resin layer is formed on the outer peripheral surface of the inner shaft.

Disclosure of Invention

When the inner and outer shafts slide relative to each other, the load of these sliding shafts may cause the resin layer to move toward the base side and tip side of the internal teeth. As a result, the contact area of the resin layer that contacts the internal teeth of the outer shaft increases, potentially leading to deterioration of the sliding characteristics.

The present invention allows the extensible shaft to undergo a smaller increase in the contact area of the resin layer with the internal teeth, resulting in less deterioration of its sliding characteristics.

One aspect of the present invention is an extendible shaft. The extendable shaft includes: an inner shaft comprising a plurality of external teeth; an outer shaft including a plurality of inner teeth that slide relative to the outer teeth; and a resin layer covering the external teeth. The pressure angle of the outer teeth is different from the pressure angle of the inner teeth.

This configuration allows the elongatable shaft to undergo a smaller increase in the contact area of the resin layer with the internal teeth, resulting in less deterioration of its sliding characteristics.

Drawings

Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and wherein:

fig. 1 is a schematic configuration diagram of a vehicle steering device having an intermediate shaft to which an extendable shaft according to an embodiment is applied;

fig. 2 is a partially cut-away side view showing the intermediate shaft according to the embodiment;

fig. 3 is a sectional view showing a cross-sectional shape of a portion of the intermediate shaft according to the embodiment;

fig. 4 is a flowchart showing a flow of a manufacturing method of the intermediate shaft according to the embodiment;

fig. 5 is an enlarged cross-sectional view showing a side of the resin layer according to the embodiment; and

fig. 6 is an enlarged cross-sectional view showing a side surface of a resin layer according to a comparative example.

Detailed Description

Embodiments will be described in detail below with reference to the accompanying drawings. The embodiments that will be described below represent a comprehensive or specific example. Numerical values, shapes, materials, constituent elements, positions of arrangement, connection forms of the constituent elements, and the like are examples, and are not intended to limit the present invention. Among the constituent elements in the following embodiments, those which are not recited in the independent claims representing the main concept will be described as optional constituent elements.

The drawings are schematic views, some parts of which are enlarged, omitted, or scaled as necessary to illustrate the present invention, and shapes, positional relationships, and scales in the drawings may be different from actual ones.

Overview of vehicle steering apparatus

Fig. 1 is a schematic configuration diagram of a vehicle steering device having an intermediate shaft to which an extendable shaft according to the present embodiment is applied. As shown in fig. 1, a vehicle steering device 1 includes: a steering shaft 3, the steering shaft 3 being coupled to a steering member 2 such as a steering wheel; and an intermediate shaft 5, the intermediate shaft 5 being an extendable shaft coupled to the steering shaft 3 through a universal joint 4; a pinion shaft 7, the pinion shaft 7 being coupled to the intermediate shaft 5 via a universal joint 6; and a rack shaft 8 as a rotating shaft, the rack shaft 8 having a rack 8a that meshes with a pinion 7a provided near an end of the pinion shaft 7.

The rack-and-pinion mechanism including the pinion shaft 7 and the rack shaft 8 constitutes a rotating mechanism a 1. The rack shaft 8 is supported by a housing (not shown) so as to be movable in an axial direction along the left-right direction of the vehicle. Each end of the rack shaft 8 is coupled to a respective turning wheel 15 through a respective tie rod and a respective knuckle arm.

The steering shaft 3 is supported on the vehicle body side by a steering column 20.

Structure of intermediate shaft

Fig. 2 is a partially cut-away side view showing the intermediate shaft 5 according to this embodiment. Fig. 3 is a sectional view taken along line III-III of fig. 2, showing a cross-sectional shape of a portion of the intermediate shaft 5 according to an embodiment.

As shown in fig. 1 to 3, the intermediate shaft 5 as an extendable shaft is formed by fitting together an inner shaft 35 and a cylindrical outer shaft 36 via splines so as to be able to slide in the axial direction X1 and transmit torque. In this embodiment, the outer shaft 36 is coupled to the universal joint 4 as an upper shaft, and the inner shaft 35 is coupled to the universal joint 6 as a lower shaft. However, the present invention is not limited to this form; either one of the inner shaft 35 and the outer shaft 36 should constitute an upper shaft, and the other should constitute a lower shaft.

Although this embodiment will be described based on the case where the extendable shaft is applied to the intermediate shaft 5, the extendable shaft of the present invention may alternatively be applied to the steering shaft 3, and the steering shaft 3 may realize the telescopic adjustment function and the shock absorbing function. Further, although the embodiment will be described based on the case where the vehicular steering device 1 is a manual steering device, the extendable shaft of the present invention may alternatively be applied to an electric or hydraulic power steering device.

An outer spline 37 is formed on the outer peripheral surface 35a of the inner shaft 35. An inner spline 38 is formed on an inner peripheral surface 36a of the outer shaft 36. The external splines 37 and the internal splines 38 are slidable in the axial direction in a state of being fitted together in the circumferential direction, and the intermediate shaft 5 is extended and retracted as a whole in a state where the inner shaft 35 and the outer shaft 36 are moved relative to each other.

Next, the inner shaft 35 will be described in detail. The inner shaft 35 has a shaft body 40 and a resin layer 50. The shaft body 40 is an elongated member along the axial direction X1. The shaft body 40 is made of a metal having a small specific gravity. Specifically, the shaft body 40 is integrally molded from aluminum or an aluminum alloy. The shaft body 40 is a cylindrical body, and an external spline 37 is formed on an outer peripheral surface thereof. At one end of the shaft body 40, a plurality of external teeth 41 are formed on an outer circumferential surface. The external teeth 41 form the external splines 37. The external teeth 41 are radially arranged around the axial center of the shaft body 40. The number of the outer teeth 41 to be provided should be at least two in the circumferential direction, but from the viewpoint of stable torque transmission characteristics, four or more outer teeth 41 are preferable.

Each outer tooth 41 extends in the axial direction X1. Therefore, the plurality of grooves 43 as portions between the outer teeth 41 in the circumferential direction also extend in the axial direction X1. Each outer tooth 41 has a tapered shape with a tip end face 42. In the external tooth 41, when the tooth thickness on the base side is the first tooth thickness t1 and the tooth thickness on the tip side is the second tooth thickness t2, the ratio (first ratio) of the second tooth thickness t2 to the first tooth thickness t1 is t2/t 1. Pressure angle α of external tooth 41 is an acute angle formed by radius line r1 of external tooth 41 and tangent line L1 with respect to the tooth surface of external tooth 41 at a point (e.g., a node) in the tooth surface.

The resin layer 50 is made of a resin material such as a polyamide resin, and covers the outer peripheral surface of each external tooth 41 (or external spline 37). Specifically, the resin layer 50 directly covers each of the outer teeth 41 and the grooves 43 to a substantially uniform thickness. The resin layer 50 gives the tooth shape of the male spline 37 a substantially uniform shape along the axial direction X1. The face of the resin layer 50 corresponding to the tip face 42 of each external tooth 41 will be referred to as a tooth tip face 59. The face of the resin layer 50 adjacent to the tip end face 59 of each tooth of the resin layer 50 will be referred to as a side face 58, and the face of the resin layer 50 corresponding to each tooth bottom will be referred to as a tooth bottom face 57.

Next, the outer shaft 36 will be described in detail. The outer shaft 36 is a cylindrical body, and has an internal spline 38 formed on an inner peripheral surface 36 a. The internal spline 38 has a plurality of internal teeth 39 that mesh with the external teeth 41, respectively. Each internal tooth 39 extends in the axial direction X1. Therefore, the plurality of tooth grooves 391 as portions between adjacent pairs of the internal teeth 39 also extend in the axial direction X1. One outer tooth 41 is disposed in each spline 391. The inner teeth 39 are tapered with a slight end face 392. In the slot 391, in the case where the width on the top side is the first groove width W1 and the width on the bottom side is the second groove width W2, the ratio (second ratio) of the second groove width W2 to the first groove width W1 is W2/W1. The pressure angle β of the inner teeth 39 is an acute angle formed by a radius line r2 of the inner teeth 39 at a point (e.g., a node) in the tooth surface and a tangent L2 to the tooth surface of the inner teeth 39. The pressure angle beta of the inner teeth 39 is smaller than the pressure angle alpha of the outer teeth 41. In other words, the pressure angle α of the outer teeth 41 is larger than the pressure angle β of the inner teeth 39. Therefore, the first ratio is smaller than the second ratio. Due to this relationship, one end portion of the tip end surfaces 392 of the internal teeth 39 is in contact with the side surfaces 58 of the resin layer 50, but there is a gap S between the side surfaces 58 and the side surfaces 393 of the internal teeth 39, the width of the gap S gradually increasing toward the radially outer side of the intermediate shaft 5.

Method for manufacturing intermediate shaft

Next, a method of manufacturing the intermediate shaft 5 as an extendable shaft will be described. Fig. 4 is a flowchart illustrating a flow of a manufacturing method of the intermediate shaft 5 according to the embodiment.

As shown in fig. 4, first, the shaft body 40 is formed by forming the external teeth 41 on the circular metal bar (teeth forming step S1). In the tooth forming step S1, the external teeth 41 are formed on the outer peripheral surface of the round bar by, for example, drawing, cutting, or the like of the round bar.

Then, resin injection molding is performed on the shaft body 40 to form the resin layer 50 (resin layer forming step S2). Specifically, in the resin layer forming step S2, the resin layer 50 is formed by injection molding that includes accommodating the shaft body 40 in a mold and injecting resin into the mold. Thereby, the resin layer 50 covering the external teeth 41 and the concave grooves 43 is formed.

Next, the shaft body 40 is cooled (cooling step S3). The cooling may be natural cooling or cooling by a cooling device. This cooling solidifies the resin layer 50.

Next, the inner shaft 35 is engaged with the outer shaft 36 having the internal splines 38 formed on the inner circumferential surface, and a dressing (smoothening) step S4 is performed. The trimming step S4 is a step of sliding the inner shaft 35 and the outer shaft 36 relative to each other to heat and melt the resin layer 50. The frictional heat generated by the relative sliding melts a part of the resin layer 50.

Fig. 5 is an enlarged sectional view illustrating a side surface 58 of the resin layer 50 according to an embodiment. Fig. 5 shows an enlarged view within circle C1 of fig. 3. In fig. 5, the shape of the side face 58 before the trimming process is indicated by a broken line. As shown in fig. 5, a gap S is left between the side surface 58 of the resin layer 50 and the side surfaces 393 of the internal teeth 39, and a part of the resin layer 50 melted in the trimming step S4 moves to the gap S and bulges out, thereby forming the bulging portion 51. The bulge 51 may partially contact the side 393 of the internal teeth 39.

Here, fig. 6 is an enlarged cross-sectional view illustrating a side surface 58a of the resin layer 50a according to the comparative example. Also in fig. 6, the shape of the side face 58a before the trimming process is indicated by a broken line. The comparative example differs from the embodiment in that the pressure angle β of the internal teeth 39 and the pressure angle α of the external teeth 41 are substantially equal. Therefore, in the comparative example, the first ratio and the second ratio are substantially equal, and therefore there is no gap S or a very small gap S as compared with the embodiment. For this reason, when the trimming step S4 is performed in the comparative example, the melted portion of the resin layer 50a moves toward the tooth tip end face 59 and the tooth bottom face 57 and bulges at two locations, thereby forming the bulging

portions

51a, 51 b. The bulging

portions

51a, 51b are in contact with the tip end surfaces 392 of the internal teeth 39 and the side surfaces 393, respectively.

In this way, in the comparative example, the bulging

portions

51a, 51b are formed at two places, but in the present embodiment, the bulging portions 51 are preferably formed in the gaps S between the side surfaces 58 of the resin layer 50 and the side surfaces 393 of the internal teeth 39, so that the formation of the bulging

portions

51a, 51b can be avoided. Therefore, the resin layer 50 that is unfavorable for torque transmission is made to experience a smaller increase in the contact area with the tip end surfaces 392 of the internal teeth 39 and the side surfaces 393 (tooth surfaces).

As described above, the manufacture of the intermediate shaft 5 includes the trimming step S4 of sliding the inner shaft 35 and the outer shaft 36 relative to each other and thereby heating and melting the resin layer 50, the trimming step S4 causing a smaller increase in the contact area of the resin layer 50 with the internal teeth 39. Therefore, it is possible to more reliably suppress deterioration of the sliding characteristics of the intermediate shaft 5 subjected to the dressing step S4. Also, in the intermediate shaft 5 that has not been subjected to the trimming step S4, when the inner shaft 35 and the outer shaft 36 slide relative to each other during normal use, a portion of the resin layer 50 melts. In this case, too, the melted portion of the resin layer 50 bulges only in the gap S, so that the increase in the contact area of the resin layer 50 with the internal teeth 39 is small. In this manner, the deterioration of the sliding characteristics of the intermediate shaft 5 that is not subjected to the dressing step S4 can also be suppressed.

Here, since aluminum or an aluminum alloy is lightweight, the use of aluminum or an aluminum alloy for the shaft body 40 can reduce the weight of the intermediate shaft 5 (extendable shaft). On the other hand, aluminum or aluminum alloys have a relatively low melting point. Therefore, when aluminum or an aluminum alloy is used for the shaft body 40 and the resin layer is applied by fluidized-bed coating, the strength of the shaft body 40 tends to become low due to the influence of heat generated during the fluidized-bed coating. However, according to the extensible shaft and the method of manufacturing the same described above, since the resin layer 50 is formed by injection molding, it is possible to avoid a decrease in strength of the shaft body 40 even if made of aluminum or an aluminum alloy.

Advantages of the invention

As described above, the ratio (first ratio) of the second tooth thickness t2 of the external teeth 41 to the first tooth thickness t1 is smaller than the ratio (second ratio) of the second groove width W2 of the spline 391 to the first groove width W1, so that the gap S can be left between the side faces 58 of the resin layer 50 and the side faces of the internal teeth 39. The portion of the resin layer 50 that melts when the inner shaft 35 and the outer shaft 36 slide relative to each other moves toward the gap S and bulges out. Therefore, the resin layer 50, which is disadvantageous in torque transmission, experiences a smaller increase in the contact area with the internal teeth 39 than the case where the resin layer 50 bulges out at two locations in the comparative example. If the increase in the contact area is small, friction occurring when the inner shaft 35 and the outer shaft 36 slide relative to each other is small, and therefore deterioration of the sliding characteristics can be suppressed.

Since the pressure angle α of the outer teeth 41 is larger than the pressure angle β of the inner teeth 39, the relationship that the first ratio is lower than the second ratio can be reliably established by adjusting only the pressure angles α, β. In the case where the pressure angle α of the outer teeth 41 is larger than the pressure angle α of the inner teeth 41 as in the embodiment, the distance from the rotation center to the meshing position can be shortened, which in turn can reduce the torque acting on the meshing position, as compared with the case where the pressure angle β of the inner teeth 39 is larger than the pressure angle α of the outer teeth 41. Therefore, the resin layer 50 bulges to a small extent toward the tip end surfaces 392 of the internal teeth 39.

Others

Although the extendable shaft and the method of manufacturing the same according to the present invention have been described above based on the embodiments, the present invention is not limited to the above-described embodiments.

For example, in the present embodiment, the relationship that the first ratio is lower than the second ratio is established by setting the pressure angle α of the outer teeth 41 to be larger than the pressure angle β of the inner teeth 39. However, the outer teeth 41 and the inner teeth 39 may have any shape that makes the first ratio lower than the second ratio.

In the above embodiment, the case where the pressure angle α of the outer teeth 41 is larger than the pressure angle β of the inner teeth 39 has been illustrated. However, even in the case where the pressure angle α of the outer teeth 41 is smaller than the pressure angle β of the inner teeth 39, the resin layer 50 experiences a slightly smaller increase in the contact area with the inner teeth 39. This means that the pressure angle a of the outer teeth 41 should at least differ from the pressure angle β of the inner teeth 39.

In the above embodiment, the case where the shaft body 40 is made of aluminum has been illustrated. However, the shaft body 40 may be made of other metals. In this case, the resin layer 50 may be formed by fluidized bed coating.

In addition, embodiments in which various modifications are made to the present embodiment, which are conceivable by those skilled in the art, and embodiments in which constituent elements and functions in the embodiments and the modifications within the scope of the gist of the present invention are arbitrarily combined are included in the present invention.

The present invention is applicable to an extendable shaft in which an outer shaft has a resin layer.

Claims

1. An extendible shaft (5), comprising:

an inner shaft (35), the inner shaft (35) comprising a plurality of external teeth (41);

an outer shaft comprising a plurality of inner teeth (39) that slide relative to the outer teeth (41); and

a resin layer (50), the resin layer (50) covering the external teeth (41), wherein the pressure angle of the external teeth (41) is different from the pressure angle of the internal teeth (39).

2. Extendible shaft (5) according to claim 1, wherein said pressure angle of said external teeth (41) is greater than said pressure angle of said internal teeth (39).